This invention relates to an electron feed structure for a flat-type luminous device, and more particularly to an electron feed structure for a flat-type luminous device adapted to display a picture image or a projected image or be used as a back light for a non-luminous display device such as a liquid crystal display device.
Conventionally, a CRT has been generally used for a character display device, a graphic display device, an image display device or the like. Unfortunately, the CRT has a disadvantage that its construction renders the thinning and/or weight-saving of a display device highly difficult. In order to solve such a problem, a flat-type luminous device was proposed which is constructed in such a manner as disclosed in Japanese Patent Application No. 200342/1988. The proposed luminous device includes an electron source arranged at the end of the luminous device and an electron feed structure comprising an electron flow guide for guiding electrons emitted from the electron source to a position opposite to a display section.
FIGS. 4(a) and 4(b) show an example of such a conventional flat-type luminous device, wherein FIG. 4(a) is a sectional view of the device and FIG. 4(b) shows an electron feed structure arranged in the device. More particularly, the flat-type luminous device generally designated at reference numeral I includes a front cover 1 made of a light-permeable insulating material such as glass or the like, a rear plate 3 made of a glass plate or the like and positioned opposite to the front cover 1 and side plates 11, which are joined together by means of a sealing material 12 such as a low-melting flit glass or the like to form an air-tight envelope.
On the inner surface of the front cover 1 is arranged a display section 2 comprising phosphor layers of desired luminous colors and anode conductors serving also as an accelerating electrode. On the inner surface of the rear plate 3 opposite to the inner surface of the front cover 1 is arranged an electron source A. Also, an electron flow guide B for guiding electrons emitted from the electron source is arranged in the envelope in a manner to be opposite to the display section 2. Between the electron flow guide B and the display section 2 is a selecting electrode section 13 for more finely carrying out the positional selection of electrons drawn out of the electron flow guide B.
The electron source A includes a filamentary cathode 4 for emitting electrons which is stretchedly arranged so as to extend along one side of the envelope, a reflecting electrode 5 arranged adjacent to the filamentary cathode 4 and serving to force out electrons emitted from the filamentary cathode 4 toward the electron flow guide B, and a combination of a drawing-out electrode 6 and a focusing electrode 7 arranged opposite to the reflecting electrode 5 with the filamentary cathode 4 being interposed between the reflecting electrode 5 and the combination and serving to draw out and focus electrons emitted from the filamentary cathode 4 to introduce the electrons into the electron flow guide B. The electron flow guide B, when it is applied to a flat-type display device, includes a front electrode 8 divided into a plurality of electrode segments in the direction of traveling of electrons emitted from the electron source A and formed with mesh-like openings and a rear electrode 9 made of a flat metal plate and divided into a plurality of electrode segments in the direction of traveling of the electrons. The electrode segments of the front electrode 8 and rear electrode 9 are arranged parallel to one another and opposite to one another at the same intervals. The electrode segments of each of the front electrode 8 and rear electrode 9 are separated, depending upon a voltage applied thereto, into a guide electrode section to which a guide voltage is applied and a deflecting electrode section to which a deflecting voltage is applied. Also, the electrode segments of the front electrode 8 and rear electrode 9 serve as both electrode sections depending upon the position selected.
Now, the manner of operation of the conventional electron feed structure constructed as described above will be described hereinafter with reference to FIGS. 4(a) and 4(b).
The electrodes constituting the electron source A each have applied thereto a predetermined voltage of, for example, 100 V or less, resulting in electrons being drawn therefrom. In the electron flow guide B, each opposite two of the electrode segments of the front electrode 8 and rear electrode 9 constituting the guide electrode sections form each set. The so-formed electrode sets have alternately applied thereto a low voltage L of, for example, 20 V and a high voltage H of, for example, 100 V from the side of the electron source A. This causes an electrostatic lens to be formed at the boundary between the focusing electrode 7 of the electron source A and the electrode segments of the front electrode 8 and rear electrode 9 nearest the electron source A in the electron flow guide B. Likewise, in the electron flow guide B, an electrostatic lens is formed at each of the boundary of each front electrode 8 and the boundary of each rear electrode 9. The so-formed electrostatic lenses serve to guide electrons emitted from the electron source A toward the other end of the electron flow guide B without diffusing the electrons and while ensuring focusing of the electrons.
The deflection of electrons traveling in the electron flow guide B toward the display section is carried out by causing the electrode segments 8b and 9a of the front electrode 8 and rear electrode 9 positioned in proximity to the position of the display section to be selected and farther away from the electron source A to serve as a deflecting electrode section. More particularly, at least one of the application of a deflection voltage L' of a level equal to or lower than the low voltage L applied to the guide electrode section such as, for example, 0 V to the electrode segments 9a of the rear electrode 9 and the application of a deflection voltage H' of a level equal to or higher than the high voltage H applied to the guide electrode section to the electron segments 8a of the front electrode 8 positioned in proximity to the position of the display section selected causes the electrons traveling in the electron flow guide, while being focused to be deflected toward the display section 2.
In the conventional flat-type luminous device constructed as described above, in the case that a deflection voltage is applied to the electrodes of the electron flow guide B, a guide voltage applied to the guide electrode section adjacent to the deflecting electrode section is either the high voltage H or the low voltage L depending upon the position of the electrode selected.
This will be more detailedly described with reference to FIGS. 5(a) and 5(b) each of which is a graphical representation showing the analysis of an electric field obtained by applying the deflection voltage L' to the electron flow guide to deflect the electrons. When the position of the display section corresponding to the electrode segment 8' of the front electrode 8 is to be selected, a deflection voltage of, for example, 0 V is applied as a guide voltage to the electrode segment 8a of the front electrode 8 farther away from the electron source A and the electrode segment 9a of the rear surface 9 positioned opposite to the front electrode segment 8' and farther away than the electrode piece 8' from the electron source A, and the high voltage H of, for example, 100 V and the low voltage L of, for example, 30 V are alternately applied as a guide voltage to the electrode segments 8, 8' and 9 of the front electrode and rear electrode.
At this time, in the case shown in FIG. 5(a), a guide voltage of 100 V is applied to the electrode segment 8 of the front electrode, so that electrons emitted from the electron source is caused to concentrically flow toward the electrode segment 8' of the front electrode. In contrast with FIG. 5(a), when the portion of the display section corresponding to the electrode segment 8' of the front electrode defined one position this side of the electron source is selected, a guide voltage of 30 V is applied to the electrode segment 8' of the front electrode. This permits electrons emitted from the electron source to flow toward the electrode segment 8 of the front electrode because the guide voltage of 100 V is applied thereto, although a part of the electrons flow toward the electrode segment 8' of the front electrode.
Thus, the application of the guide voltage and deflection voltage to the electron flow guide as described above causes both the application of the high voltage H to the electrode segment 8' of the front electrode and the application of the low voltage thereto. This causes the correlation between the guide voltage and the deflection voltage around the position of the electron flow guide B selected to be varied depending upon the position, resulting in varying the amount of electrons drawn toward the display section. Also, this leads to a disadvantage of varying the focusing of electrons near the electrode segment 8' of the front electrode.
Further, such disadvantages are encountered when the deflection voltage H' is applied to the electrode segment 8a of the front electrode positioned near the position of the electron flow guide selected, because the correlation between the guide voltage and the deflection voltage is varied depending upon the position.